Apparatus and method for determining a measure for the solid content of a liquid toner, and printing system including such an apparatus

Abstract

A measurement apparatus for determining a measure for the solid content of a liquid toner. The liquid toner includes a carrier liquid with marking particles, and the solid content is the ratio of the mass of the marking particles divided by the mass of the liquid toner. The measurement apparatus includes a measurement space for receiving liquid toner. The measurement space includes at least one hydrostatic pressure sensor configured and arranged for measuring data representative for the hydrostatic pressure caused by the liquid toner at least one predetermined position in the measurement space. The measurement apparatus also includes a controller configured for receiving the measured data and for determining a measure for the solid content of the liquid toner based on the received data.

The invention claimed is: 
     
       1. A measurement apparatus for determining a measure for the solid content of a liquid toner, said liquid toner comprising a carrier liquid with marking particles, and said solid content being the ratio of the mass of the marking particles divided by the mass of the liquid toner, said measurement apparatus comprising:
 a measurement space for receiving liquid toner, said measurement space comprising at least one hydrostatic pressure sensor configured and arranged for measuring data representative for the hydrostatic pressure caused by the liquid toner at least one predetermined position in the measurement space; and 
 a controller configured for receiving the measured data and for determining a measure for the solid content of the liquid toner based on the received data; 
 further comprising a liquid toner reservoir storing the liquid toner; said liquid toner reservoir having an outlet line for discharging liquid toner into said measurement space and a return line for receiving liquid toner from said measurement space; 
 wherein the outlet line or the return line includes a pump, and wherein the controller is configured for controlling the pump such that normal pump operation is stopped or such that pump power is reduced while measuring data with the at least one hydrostatic pressure sensor. 
 
     
     
       2. The measurement apparatus of  claim 1 , wherein the controller is configured for controlling the pump such that normal pump operation is stopped or pump power is reduced a predetermined period of time before the measuring of data with the at least one hydrostatic pressure sensor is started, and such that the normal pump operation is only restarted after the measuring. 
     
     
       3. The measurement apparatus of  claim 1 , wherein the measurement space comprises a measurement column with a bottom end comprising an inlet for receiving the liquid toner and with an open top end in contact with the atmosphere; wherein said at least one hydrostatic pressure sensor is located in said measurement column at a distance of said open top end. 
     
     
       4. The measurement apparatus of  claim 3 , wherein said measurement space further comprises an overflow reservoir for receiving liquid toner flowing over said open top end. 
     
     
       5. The measurement apparatus of  claim 1 , wherein said measurement space has a cross section with a largest dimension which is smaller than 10 cm. 
     
     
       6. The measurement apparatus of  claim 1 , wherein the at least one sensor comprises a first sensor at a first position and a second sensor at a second position, said first and second position being in the liquid toner at a first height and a second height of a liquid column, respectively. 
     
     
       7. The measurement apparatus of  claim 1 , wherein the measurement space is provided in a liquid toner reservoir storing liquid toner; said measurement space being in fluid communication with the liquid toner reservoir. 
     
     
       8. The measurement apparatus of  claim 1 , wherein said measurement space is a gastight vessel. 
     
     
       9. The measurement apparatus of  claim 1 , wherein the measurement space is delimited by a first electrode and a second electrode, and the measurement apparatus further comprises characterizing means configured for determining a measure for the conductivity of the liquid toner based on a voltage applied between the first and the second electrode or based on a current sent through the liquid toner between the electrodes. 
     
     
       10. The measurement apparatus of  claim 1 , further comprising a temperature sensor for sensing a measure for the temperature of the liquid toner in the measurement space, wherein the controller is further configured for taking into account the sensed measure for the temperature when determining the measure for the solid content of the liquid toner based on the received data. 
     
     
       11. A printing system comprising:
 a printing apparatus with a toner feed unit and a toner recuperation line, and 
 an apparatus according to  claim 1 , wherein the liquid toner reservoir of said apparatus has an outlet for discharging stirred liquid toner to the printing apparatus, and an inlet; said outlet being connected to the toner feed unit of the printing apparatus, and said inlet being connected to the toner recuperation line. 
 
     
     
       12. A measurement apparatus for determining a measure for the solid content of a liquid toner, said liquid toner comprising a carrier liquid with marking particles, and said solid content being the ratio of the mass of the marking particles divided by the mass of the liquid toner, said measurement apparatus comprising:
 a measurement space for receiving liquid toner, said measurement space comprising at least one hydrostatic pressure sensor configured and arranged for measuring data representative for the hydrostatic pressure caused by the liquid toner at least one predetermined position in the measurement space; and 
 a controller configured for receiving the measured data and for determining a measure for the solid content of the liquid toner based on the received data; 
 wherein said measurement space has a height which is larger than 20 cm. 
 
     
     
       13. A measurement apparatus for determining a measure for the solid content of a liquid toner, said liquid toner comprising a carrier liquid with marking particles, and said solid content being the ratio of the mass of the marking particles divided by the mass of the liquid toner, said measurement apparatus comprising:
 a measurement space for receiving liquid toner, said measurement space comprising at least one hydrostatic pressure sensor configured and arranged for measuring data representative for the hydrostatic pressure caused by the liquid toner at least one predetermined position in the measurement space; 
 a controller configured for receiving the measured data and for determining a measure for the solid content of the liquid toner based on the received data; 
 wherein the measurement space is provided in a liquid toner reservoir storing liquid toner; said measurement space being in fluid communication with the liquid toner reservoir; 
 wherein the liquid toner reservoir is provided with a stirring means, and wherein the controller is configured for stopping the stirring operation performed by the stirring means a predetermined period of time before the measuring of data with the at least one hydrostatic pressure sensor is started, and such that the stirring operation is only restarted after the measuring. 
 
     
     
       14. A method for determining a measure for the solid content of a liquid toner, said liquid toner comprising a carrier liquid with marking particles, said solid content being the ratio of the mass of the marking particles divided by the mass of the liquid toner; said method comprising:
 receiving liquid toner in a measurement space; 
 measuring data representative for the hydrostatic pressure caused by the liquid toner at least one predetermined position in the measurement space; and 
 receiving the measured data at a controller and for determining a measure for the solid content of the liquid toner based on the received data; 
 said method further comprising storing liquid toner in a liquid toner reservoir; discharging liquid toner using a pump into said measurement space, stopping the pump operation during the measuring, and returning liquid toner using said pump from said measurement space to the liquid toner reservoir after said measuring. 
 
     
     
       15. The method of  claim 14 , wherein the measurement space comprises a measurement column with a bottom end comprising an inlet for receiving the liquid toner and with an open top end in contact with the atmosphere; wherein the hydrostatic pressure is measured at a distance of said open top end. 
     
     
       16. The method of  claim 15 , further comprising storing liquid toner in a liquid toner reservoir while stirring the liquid toner, wherein the measurement space is provided in the liquid toner reservoir storing liquid toner; and wherein the controller stops the stirring during the measuring, and restarts the stirring after the measuring. 
     
     
       17. The method of  claim 14 , further comprising sensing a measure for the temperature of the liquid toner in the measurement space, and taking into account the sensed measure for the temperature when determining the measure for the solid content of the liquid toner based on the received data.